Shortened horn antenna with multiple phased feed



Aug. 25, 1964 B. G. HAGAMAN SHORTENED HORN ANTENNA WITH MULTIPLE PHASEDFEED Filed Aug. 24, 1959 Tltil..-

I NVENTO R Bowvmv /hq/amm/ ATTORNEY6 United States Patent 3,146,453SHORTENED HQRN ANTENNA WITH MULTIPLE PHASE!) FEED Boynton G. Hagaman,Falls Church, Va., assignor, by

mesne assignments, to Deco Electronics, Inc., Washington, D.C., acorporation of Virginia Filed Aug. 24, 1959, Ser. No. 835,730 7 Claims.(Cl. 343778) The present invention relates to electromagnetic hornantennas and particularly to the reduction of the length of suchantennas and the improvement of their operating efiiciency.

It is known that the flare angle of electromagnetic horns must be keptrather small by increasing their length relative to the width of theaperture, otherwise the waves arrive at the aperture in differentphases, thereby decreasing the radiation efficiency of the horn andreducing its directivity. For this reason as well as the fact that theradiating aperture of the horn must generally have a width equal toseveral wave lengths, horns have been used in the past only for veryshort wavelengths and particularly for microwaves. When horn antennasare used for wavelengths of as much as a hundred meters, or even more,the dimensions of the horn and particularly its length become verygreat. Horns of such size are expensive to construct and maintain andrequire a very large land area. The large length of an efiicient horn isa drawback also at shorter wavelengths, particularly where only alimited antenna mounting area is available or where there are windresistance difficulties and other problems due to the size of theantenna. For all these reasons it is obviously important to reduce thelength of a horn antenna without impairing its operating efliciency, orconversely, to improve the operating eificiency of a given horn antenna.

According to the present invention, the length of a horn antenna can bereduced considerably or its aperture efiiciency adjusted. This isaccomplished by exciting the antenna with waves having difierent phaserelationships such that after the waves travel different distances tothe radiating aperture of the antenna, they arrive at the aperture atcontrollably diiferent phases, or nearly in the same phase so as toenable the antenna to maintain a high radiation efiiciency. An object ofthe invention is to accomplish this result without impairing orobstructing the transmission of waves through the horn.

Another object of the invention is to vary or adjust the apertureefliciency of a horn antenna, and consequently its beamwidth ordirectivity, over a considerable range by adjusting the relative phasedelay between the waves in a center feed section and end feed sectionsof the horn.

Other objects and advantages of the invention will become apparent andthe invention will be fully understood from the following descriptionand the drawings in which:

FIG. 1 is a top view of the antenna with a portion of y the wave guidewall broken away;

FIG. 2 is a side view of the horn antenna; and

FIG. 3 is a view looking into the aperture of the horn.

The invention will be described particularly with respect to a hornantenna of the type disclosed in my co-pending application, Serial No.791,248, now Patent No. 2,992,429. Antennas of this type may be used forrelatively long wavelengths of a hundred meters or even more. Suchantennas, of course, have dimensions of many hundred feet and require anextensive supporting arrangement, which is not a part of the presentinvention and not necessary to a full understanding thereof. It may alsobe noted that antennas of this size and intended for rather longwavelengths need not be constructed of solid metallic material but mayconsist of metallic mesh or wires.

3,146,453 Patented Aug. 25, 1964 The particular horn shown in thedrawing has a polygonal aperture the maximum dimensions of which are inhorizontal and vertical planes. The horn 10 has eight triangular sides11-18 forming a flared horn with a square aperture. It will beunderstood, of course, that other types of horns of known design andconstructed in vari ous ways may be used. It will be assumed that it isdesired to utilize the horn for transmission, although it will beunderstood that the same antenna can also be used for reception and thatthe antenna is to be excited with waves having a horizontalpolarization.

Opposite the aperture 20 the small end 21 of the horn is connected to awave guide 22. The wave guide is herein shown as a rectangular guide. Aplurality of partitions 24, 26 formed of metal divide the wave guideinto a plurality of separate compartments. Partitions or walls 24, 26are in vertical planes. Each compartment or section 27, 28, 29 of thewave guide is separately energized by waves from the same source 30. Theapparatus 30 may, of course, be a receiver, when the horn is being usedfor radio reception. The translating apparatus 30 is connected by aplurality of feed lines 32, 34 and 36 to horizontally extendingradiators 38, 40 and 42. Radiators 38, 40 and 42 may be any suitableantennas, such as linear probes extending horizontally for producinglinearly polarized Waves in the several sections of wave guide 2.0. Feedline 34 includes a preferably adjustable delay device or delay line 44connected to the radiator 40.

When waves are supplied from source 30 by lines 32, 34 and 36 and delaydevice 44 to the wave guide 22, the waves arrive at antennas 40 insection 28 with a given delay relative to the waves produced in waveguide sections 27 and 29. The waves emanating from the wave guidesection 28 travel an approximate distance L to the aperture 20 along thecentral portion of the horn while the Waves in wave guide sections 27and 29 travel a greater distance indicated by R along the sides of thehorn to the end of the aperture. The longer wave length path R producesa phase delay with respect to the wave travelling the shorter path L.This phase delay is compensated by the delay introduced by the delayline 44. Thus, by the use of only one delay device connected to thecentral radiator 40 a considerable correction of the phase variationacross the aperture 20 can be accomplished, thereby increasing theradiation efficiency and the directivity of the horn, and permitting thehorn to have a short length. Adjustment of delay device 44 permits theaperture efliciency to be controlled. Inasmuch as the directivity orbeamwidth of the horn is related to its aperture efficiency, the delaydevice 44 constitutes a means of varying the directivity of the hornover a considerable range. This variation of beamwidth is extremelyadvantageous where it is desired to cover a large or small target withthe same antenna.

It will be understood that I have described the invention in itssimplest form, and it will be quite apparent to those skilled in the artthat the Wave guide 22 might be divided into any number of separatesections and that any number of exciting antennas might be placed ineach section. Since many variations and modifications of my inventiondisclosed herein will be apparent to those skilled in the art, theinvention is not to be construed as limited except as defined in thefollowing claims.

What is claimed is:

1. An electromagnetic wave antenna comprising a flared horn having ashort length and an aperture lying in a given plane, a rectangular waveguide connected to the small end of said horn, said wave guide having aplurality of longitudinally extending metallic walls dividing the waveguide into inner and outer sections, whereby the inner wave guidesection illuminates predominantly .he middle portion of the hornaperture and outer sections of the wave guide illuminate predominantlythe end portions of the horn aperture, a source of radio waves, meansfor supplying the radio waves from said source to said wave guide, andmeans for compensating for the relative phase differences between Wavesarriving at the aperture of said horn, said compensating meanscomprising means for delaying the waves supplied from said source to theinner Wave guide section relative to the waves supplied to said outerwave guide sections.

2. An antenna comprising a flared horn having a short length and anaperture lying in a single plane, a rectangular wave guide connected tothe small end of said horn, said wave guide having a plurality oflongitudinally extending metallic partitions dividing it intointermediate and outer wave guides, a first exciting means in saidintermediate wave guide for illuminating predominantly the middleportion of the horn aperture and additional exciting means in said outerwave guides for illuminating the peripheral portions of the hornaperture, a source of radio waves, means for supplying the radio wavesfrom said source to said exciting means, and means for cornpensating forthe relative phase differences between waves arriving at the aperture ofsaid horn, said compensating means comprising means for delaying thewaves supplied from said source to the first exciting means relative tothe waves supplied from the source to said additional exciting means.

3. An antenna according to claim 2, wherein said exciting means includeparallel linear radiators extending perpendicularly to said partitions.

4. An antenna according to claim 3, the horn being formed and fixed tosaid Wave guide so that the width of the aperture in the directionperpendicular to said linear radiators is a maximum at the middlethereof and tapers to minimum values at the ends of the aperture.

5. In combination, a flared horn having a large flare angle and a shortlength, a rectangular wave guide connected to the small end of saidhorn, said wave guide including a first antenna means including a linearradiator coupled predominantly to the middle portion of the hornaperture and additional antenna means including linear radiators coupledpredominantly to the end portions of the horn aperture, radio wavetransmission means connected to said antenna means, and means forcompensating for the relative phase difierences between waves arrivingat the aperture of said horn, said compensating means comprising meansfor delaying the waves supplied to the first antenna means relative tothe Waves supplied to said additional antenna means, the horn beingformed so that the width of the aperture in the direction perpendicularto said linear radiators is a maximum at the middle thereof and tapersto minimum values at the ends of the aperture.

6. In combination, a flared horn having at least two relatively rapidlydiverging walls, a wave guide connected to the small end of said horn,said Wave guide including first wave supply means communicatingpredominantly with the middle portion of the horn, and additional wavesupply means communicating predominantly with the portions of the hornadjacent said diverging Walls, radio wave transmission means connectedto said wave supply means, and means for compensating for the relativephase differences between Waves arriving at the aperture of said horn,said compensating means comprising means for producing a phase delay inthe waves supplied to the first wave supply means relative to the wavessupplied to said additional wave supply means, said delay beingproportional to the difference between the length of said middle portionand the length of said end portions.

7. An antenna according to claim 6, wherein said waveguide is of arectangular cross-section and said horn comprises eight triangularsides, the bases of four of said sides being fixed to respective Wallsof said Waveguide.

References Cited in the file of this patent UNITED STATES PATENTS2,245,660 Feldman June 17, 1941 2,283,935 King May 26, 1942 2,438,735Alexanderson Mar. 30, 1948 2,438,987 Bailey Apr. 6, 1948 2,692,336 KockOct. 19, 1954 2,743,440 Riblet Apr. 24, 1956 2,897,491 Young July 28,1959

1. AN ELECTROMAGNETIC WAVE ANTENNA COMPRISING A FLARED HORN HAVING ASHORT LENGTH AND AN APERTURE LYING IN A GIVEN PLANE, A RECTANGULAR WAVEGUIDE CONNECTED TO THE SMALL END OF SAID HORN, SAID WAVE GUIDE HAVING APLURALITY OF LONGITUDINALLY EXTENDING METALLIC WALLS DIVIDING THE WAVEGUIDE INTO INNER AND OUTER SECTIONS, WHEREBY THE INNER WAVE GUIDESECTION ILLUMINATES PREDOMINANTLY THE MIDDLE PORTION OF THE HORNAPERTURE AND OUTER SECTIONS OF THE WAVE GUIDE ILLUMINATE PREDOMINANTLYTHE END PORTIONS OF THE HORN APERTURE, A SOURCE OF RADIO WAVES, MEANSFOR SUPPLYING THE RADIO WAVES FROM SAID SOURCE TO SAID WAVE GUIDE, ANDMEANS FOR COMPENSATING FOR THE RELATIVE PHASE DIFFERENCES BETWEEN WAVESARRIVING AT THE APERTURE OF SAID HORN, SAID COMPENSATING MEANSCOMPRISING MEANS FOR DELAYING THE WAVES SUPPLIED FROM SAID SOURCE TO THEINNER WAVE GUIDE SECTION RELATIVE TO THE WAVES SUPPLIED TO SAID OUTERWAVE GUIDE SECTIONS.